Chapter 6: Habitat Suitability

SHORT SUMMARY:

Chapter 6 looks at the effect of ecosystems on sea otters. Assessing critical habitat features in Oregon that will determine whether those habitats can support sea otter populations in the future is known as a habitat suitability analysis. Such an analysis represents an important step in 1) selecting prospective sites for any future reintroduction efforts, 2) assessing the areas where sea otters are most likely to concentrate in the future, and 3) identifying where sea otters might come into potential conflict with human activities.

Sea otter occurrence in nearshore marine habitats depends on depth and slope, substrate composition, prey abundance and primary productivity, coastal geography, and sea otter behavior and social structure. All of these features contribute to the spatial variation in sea otter distribution and abundance. Essentially, all coastal habitats within their geographic range can be considered potentially suitable habitat. It appears that sea otters make use of all coastal areas in regions where they have fully recovered since the fur trade; however, not all nearshore habitats support equal densities of sea otters. For example, in both California and Southeast Alaska, local equilibrium densities of sea otters varied more than 20-fold based on habitat differences. In short, the characteristics of existing habitat in Oregon will influence reintroduction efforts.

Based on the abundance and distribution of existing sea otter populations in coastal habitats around the north Pacific, it seems likely that all of coastal Oregon (including estuaries) represents potentially suitable sea otter habitat. However, there is considerable variation in habitat features throughout the state—benthic substrate (and associated invertebrate prey communities), kelp canopy cover along the outer coast, eelgrass beds in estuaries—and certain areas may provide higher quality habitat for sea otters.

In terms of outer coast habitats, areas in the southern half of the state appear to have a higher abundance of preferred habitat features and prey populations (especially urchins): in particular, the reef complexes near Port Orford (Blanco Reef, Orford Reef, and Redfish Rocks) and Cape Arago (Simpson reef), and in the central part of the state (Depoe Bay/Yaquina Head). In terms of estuarine habitats, three larger estuaries appear to have an optimal combination of prey resources (clams, crabs) and resting habitats (eelgrass beds, tidal creeks), which suggests they could potentially support viable sea otter populations: Tillamook Bay, Yaquina Bay, and Coos Bay. The latter two have the additional advantage of proximity to outer coast reefs and kelp beds that could provide alternative habitats for establishing sea otter populations.